Spinal Cord Injury or Compression: This is the most likely diagnosis due to the sudden onset of leg weakness and bowel incontinence, which are common symptoms of spinal cord damage. The spinal cord controls both motor functions, such as walking, and autonomic functions, including bowel control.

Stroke: Although less common for causing bowel incontinence directly, a stroke affecting the spinal cord (spinal stroke) or the brain's areas controlling these functions could lead to similar symptoms.
Multiple Sclerosis: An acute relapse of multiple sclerosis could cause sudden neurological deficits, including leg weakness and bowel dysfunction, due to demyelination in the central nervous system.
Guillain-Barré Syndrome: This autoimmune disorder can lead to rapid-onset muscle weakness and, in some cases, autonomic dysfunction, which might include bowel incontinence.

Cauda Equina Syndrome: A medical emergency where the nerves in the spinal canal are compressed, leading to loss of bladder and bowel control, as well as leg weakness. Prompt surgical intervention is often necessary.
Spinal Epidural Abscess: An infection that can compress the spinal cord, leading to neurological deficits. It requires urgent diagnosis and treatment to prevent permanent damage.
Traumatic Injury: Any recent trauma could have caused a spinal injury leading to these symptoms, and immediate assessment is crucial.

Neurosyphilis: A late manifestation of syphilis infection that can affect the spinal cord, leading to various neurological symptoms, including leg weakness and bowel dysfunction.
Vitamin B12 Deficiency: Severe and prolonged deficiency can lead to subacute combined degeneration of the spinal cord, causing weakness, gait disturbances, and bowel/bladder dysfunction.
Tumors (Spinal or Brain): Although less common, tumors can compress or invade the spinal cord or brain areas responsible for these functions, leading to similar symptoms.